AWS Welding Defects & Quality Control 2 — Questions and Answers

Question 1: A weld with excessive convexity (high crown) is problematic because:

It wastes filler metal but has no structural consequence
It creates stress concentration at the weld toes and may indicate improper deposition technique (Correct answer)
It makes slag removal more difficult
It indicates insufficient penetration

Correct answer: It creates stress concentration at the weld toes and may indicate improper deposition technique

Excessive weld convexity creates a sharp geometric notch at the weld toes (junction between weld face and base metal), which concentrates stress and significantly reduces fatigue life under cyclic loading.

The weld toe is a geometric discontinuity — a transition from the weld surface to the base metal. Excessive convexity creates a steep angle at this transition (high stress concentration factor Kt). Under static loading, mild convexity is generally acceptable; under cyclic/fatigue loading, the toe stress concentration dominates fatigue crack initiation. AWS D1.1 limits weld convexity (e.g., fillet weld convexity ≤1/16 inch plus 0.10 × weld face width). Excessively convex welds may also indicate: too low voltage, too fast travel speed, incorrect weaving technique, or electrode type issues.

Question 2: Incomplete joint penetration (IJP) in a groove weld is distinguished from incomplete fusion by:

IJP is a surface defect; incomplete fusion is a subsurface defect
IJP is failure to achieve the specified joint penetration depth at the root; incomplete fusion is lack of bonding between weld and base metal at any location (Correct answer)
They are the same defect with different names in different codes
IJP only occurs in fillet welds; incomplete fusion only in groove welds

Correct answer: IJP is failure to achieve the specified joint penetration depth at the root; incomplete fusion is lack of bonding between weld and base metal at any location

IJP specifically refers to inadequate penetration depth at the root of the joint (root pass doesn't reach the specified root depth), while incomplete fusion refers to any lack of bonding between weld metal and base metal at any interface in the joint.

AWS D1.1 distinguishes these defects: Incomplete joint penetration (also called lack of penetration or LOP) occurs when the root pass fails to achieve the required depth of fusion — a gap exists at the joint root. It is common in single-sided welds where root pass energy was insufficient, groove angle was too narrow, or root face too large. Incomplete fusion (LOF) can occur anywhere in the joint — at the fusion line, between passes, or at the root — wherever the weld metal fails to bond to the base metal or previous pass. Both are rejectable under D1.1 visual and NDE criteria due to their stress-concentrating, crack-initiating nature.

Question 3: The Brinell Hardness Number (BHN) for typical E7018 deposited weld metal is approximately:

50–80 BHN (very soft — below base metal)
150–200 BHN (typical for as-deposited carbon steel weld metal) (Correct answer)
300–350 BHN (moderately hard)
500+ BHN (harder than hardened tool steel)

Correct answer: 150–200 BHN (typical for as-deposited carbon steel weld metal)

As-deposited E7018 weld metal typically has a hardness in the 150–200 BHN range, compatible with the 70 ksi yield strength and ductile properties it is designed to provide.

Hardness correlates with tensile strength (approximately: BHN × 0.5 = tensile strength in ksi for steel). E7018 weld metal with ~75 ksi ultimate tensile strength corresponds to ~150–200 BHN. The HAZ immediately adjacent to the fusion line in hardenable steel is often harder (250–400 BHN) due to rapid quenching. Carbon equivalent (CE) and cooling rate determine HAZ hardness. AWS D1.1 and pressure vessel codes (ASME B31.3) limit HAZ hardness to prevent embrittlement: typically 248–325 BHN maximum depending on service environment. Hardness testing (Vickers HV10 or Brinell BHN) is part of WPS qualification for corrosive service applications.

Question 4: During radiographic testing (RT) of a weld, the image quality indicator (IQI) or penetrameter is used to:

Measure the radiation dose received by the welder
Verify that the radiographic technique has sufficient sensitivity to detect minimum rejectable discontinuities (Correct answer)
Indicate the weld location on the film for traceability
Measure the exact size of detected defects

Correct answer: Verify that the radiographic technique has sufficient sensitivity to detect minimum rejectable discontinuities

The IQI (penetrameter) verifies that the RT technique has adequate sensitivity — that discontinuities at or above the minimum rejectable size would be detectable on that specific radiograph.

AWS D1.1 Clause 6.12 specifies RT procedure requirements including IQI placement and acceptance. Two types: wire IQI (set of wires of decreasing diameter per ASTM E747) and hole IQI (plaque with drilled holes). The visible wire or hole indicates the minimum detectable discontinuity size for that film/source/technique combination. If the required IQI sensitivity wire/hole is not visible on the radiograph, the technique is inadequate and must be improved (different film type, geometry, energy level). IQI does not measure defect size — it qualifies the sensitivity of the technique.

Question 5: Weld distortion (angular and longitudinal) is best controlled during fabrication by:

Increasing heat input to slow the cooling rate
Pre-setting (presetting parts in opposite direction of expected distortion), balanced welding, and minimizing weld volume (Correct answer)
Post-weld heating to anneal residual stresses
Using SMAW instead of GMAW for all structural welds

Correct answer: Pre-setting (presetting parts in opposite direction of expected distortion), balanced welding, and minimizing weld volume

Pre-setting parts against expected distortion, using balanced welding sequences (both sides of joint, backstep), and minimizing weld metal volume through proper joint design are the most effective distortion control methods.

Weld distortion results from uneven expansion and contraction of weld metal and HAZ during the weld thermal cycle. Control strategies: (1) Pre-setting: clamp or tack parts in a position that is the mirror image of expected distortion — the weld pulls them into final alignment; (2) Balanced welding: deposit on alternating sides of the neutral axis, canceling shrinkage forces; (3) Minimize joint volume: reduce groove angle, increase root face, use double-sided joints instead of single-sided; (4) Backstep technique: weld in short segments opposing travel direction, limiting localized heat accumulation; (5) Jigs and fixtures: restrain the workpiece. PWHT (stress relief) reduces residual stress but doesn't remove already-occurred distortion.

Question 6: Under ASME Section IX, an essential variable for welder performance qualification is defined as:

Any variable that affects weld appearance
A variable whose change requires re-qualification of the welder (Correct answer)
A variable that must be listed in the WPS but doesn't affect qualification
The welding current range — the only essential variable

Correct answer: A variable whose change requires re-qualification of the welder

An essential variable in ASME Section IX is a variable whose change requires the welder to be re-tested and re-qualified — its change significantly affects the ability of the welder to deposit sound welds.

ASME Section IX QW-350 defines essential variables for welder performance qualification. Changes to essential variables require new qualification testing: change of welding process (SMAW to GTAW); change from backing to no backing (open root requires more skill); change of base metal group (P-number change); change of filler metal group (F-number); change from downhill to uphill vertical progression; and deletion of backing gas. Non-essential variable changes (wire diameter, current within ranges, etc.) do not require re-qualification but must still comply with the WPS. Essential variables differ between ASME Section IX and AWS codes.

AWS Welding Defects & Quality Control 2

A weld with excessive convexity (high crown) is problematic because: